I think I have a parting problem........

Most if not all small LATHES will never part off a piece of metal. My reason for saying this they lack the strength to keep the parting blade from flexing. First the tool rest moves , compound flexes , the cross slide moves the ways even torque over. If you ever expect to part you will need the tool blocked up from the ways with a roller bearing to support the blades movement up to the point of just touching the piece to be cut . Rigid as possible no flexing at all then the blade still will flex and may break. I'm in the design stage of making a rotating saw blade mounted to the tool post , like a grinder , only mounted in a qctp with air fitting . My thinking with the lathe turning and blade turning no flex of any amount should make much difference. I'm letting the cat out of the bag but I'm sure it works.

With all due respect, I have to disagree, Silverbullet. I have an Emco 11" lathe that parts everything I turn with a HSS P-type blade or an Aloris GTN3 inserted carbide blade. My little Sherline can part anything that will fit in the lathe using a P1-N blade mounted upside down in a rear mounted parting tool post. In fact, the Sherline will part mild steel at 1200-1500 rpm and will cut 303 stainless washers 0.010" thick without any issues at all.

A sharp blade mounted perpendicular to the work with the tip at center height will part easily on most lathes, small or big. I think the biggest problem for most guys is that what they think is center height is not really center height; a bit high and it won't cut; a bit low and it digs in a snaps the blade. A positive feed is also important.
 
You should have no trouble parting with your PM-1340GT. What RPM are you parting at? Are you using the power feed? Most problems I see people having are not on center and running the speed/feed too slow.

Assuming the tool is set at the correct height and is square to the part. Keep the tool length to the minimum required to make the cut and try and keep the tool stick out to max 2x the blade height. For the HSS try 0.003 to 0.004 feed at 100 SFM. For the insert tool try using the power feed at 0.004 to 0.005 at 100 to 200 SFM. Remember your cross feed is 1/2 the chart setting. Parting needs lots of fluid. I use kerosene for aluminum and dark cutting oil for steel, constantly and generously applied with a small brush or squirt bottle.

Also keep the compound slide retracted and locked. I usually also lock the carriage.
 
Dan,

Are you hand feeding? What RPM are you turning? last question, is the insert clamp tight on the Kennametal?

This last time was at 240 rpm and I've only tried hand feeding. The clamp on the Kennametal was tight. After the fact, when I was re-aligning the tool post as it had moved slightly, I noticed that the compound wasn't locked. That might have been the cause.
 
Yea, I didn't want to ask basic questions as I know your on it. Rigidness is your friend for this operation. The RPMs are fine even a little higher is ok, but the tool post should be tight and minimal over hang with the compound locked out. I rarely used to lock my compound but always keep the tool post from overhanging and use CXA on the 1440. Another thing I practice after lining thing up square and centered to the work piece is looking or studying the chip produced upon introduction of the cutter. This will reveal any issues with alignment. I had parting issues off and on but these steps are crucial on smaller machines to include mine. You might also lock out the carriage when parting and use a steady drip of cutting fluid. Your chips should curl nicely and evenly when all is happy. Good luck amigo!
 
Definitely use the power feed. Hand feeding is difficult to get the feed rate correct and consistant. Its okay for smaller work.

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I don't power feed, always afraid it might dig in, by hand feeding I get feedback. Just my opinion
 
I recently got a bigger lathe 12 x 36 and was very pleased at how easily it parted until the other day when I was having a nightmare trying to part a 1/2" diameter piece of steel. So I checked out some parting videos on Youtube and in one of TubalCain's vid's I noticed he said to never part hot rolled steel, "it's a nightmare". I checked and sure enough that is what I was trying to part. The next few pieces of steel I parted went fine. But I usually don't know what I'm working with since most of it comes from the scrap yard. I did however know these pieces were hot rolled since I got them from the local hardware store. No place near me to get steel and it seems that any project I want to start needs a selection of shapes and sizes and material types I don't have. So I make due with what is on hand. Sometimes it doesn't produce the best product but I'm still learning.:)
 
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